<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

    <script>

        var en = encodeURI("我是编码之前的样子");
        document.write(en + "<br>");

        var de = decodeURI("%E6%88%91%E6%98%AF%E7%BC%96%E7%A0%81%E4%B9%8B%E5%89%8D%E7%9A%84%E6%A0%B7%E5%AD%90");
        document.write(de);


        var str = "alert(12313123)";

        eval(str);

    </script>
</head>
<body>

</body>
</html>